H E A T R E C O V E R Y I N T H E I N C I N E R A T I O N O F H O S P I T A L W A S T E S

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eat Recovery SystemsVol. 4, No. 5, pp. 385-388, 1984 0198-7593/84 3.00 + .00

Printed in Great Britain Pergam on Press Ltd

H E A T R E C O V E R Y I N T H E I N C I N E R A T I O N

O F H O S P I T A L W A S T E S

J. A. BOAVIDA

R O Q U E

and J . M.

G R A ~ A

ROCHA

D i r e c q a o - G e r a l d a s C o n s t r u ¢ 6 e s H o s p i t a l a r e s, L i s b o a , P o r t u g a l

a n d

A . C A N N A D A P IE D A D E

I n s t i t u t o S u p e r i o r T 6 c n i c o

A b s t r a c t - - T h e d e v e l o p m e n t o f t h e e n e r g y c ri s is h a s i n c r e a s ed t h e t r e n d o f t h e n e e d t o r e c o v e r e n e rg y ,

n a m e ly in th e b u i ld in g s e c to r , wh e r e s u c h r e c o v e r y c o u ld s h o w s o me in te r e s t in g a s p e ct s .

I n t h e c a s e o f h o s p it a l s , o n e o f t h e p o s s i b le m e t h o d s o f h e a t e c o n o m y c o u l d b e t h e r e c o v e r y o f w a s te

g a s h e a t r e s u l t i n g f r o m t h e i n c i n e r a t i o n o f w a s t e s ( t h i s i n c i n e r a t i o n b e i n g m a n d a t o r y d u e t o h y g i e n i c

reasons) .

I n th e p r e s e n t t e x t , t h e e c o n o m ic a l f e a s ib i li ty o f s u c h wa s te g a s h e a t r e c o v e r y , is s h o wn , b e in g in

th e o r d e r o f 6 0 % o f th e e c o n o mie s r e s u l t in g wh e n s u c h g a s i s u s e d to h e a t wa te r . A l s o , r e c o v e r y p la n t s

i n s t a l l e d i n P o r t u g u e s e h o s p i t a l s a r e d e s c r i b e d , a n d c o n s i d e r i n g o n e o f t h e m - - t h e o n l y o n e p r e s e n t l y

w o r k i n g - - a c r i t i c a l a n a l y s i s i s m a d e o f i t s p e r f o r m a n c e , a n d a l s o o f t h e c r i t e r i a b e i n g u s e d t o c o p e

w i t h t h e p r o b l e m s t h a t h a v e s o f a r a p p e a r e d .

I N T R O D U C T I O N

G arb ag e h a s a l w ay s b een t h e u n w e l co m e co m p an i o n o f M an , w h o i n h i s d a i l y l i f e g en e ra t e s t h e

accu m u l a t i o n o f fo o d w as t e s , p ack ag es o f co n su m e d a r ti c le s an d r e s id u es f ro m h i s w o rk .

W i t h th e In d u s t r ia l R ev o l u t i o n an d w i th t h e d ev e l o p m en t o f u rb an cen t er s , th e p ro b l em h as

i n c rea sed , n o t o n l y d u e t o t h e h ig h e r am o u n t an d co n cen t r a t i o n o f th e r e s id u es , b u t a lso d u e t o

the change o f i ts charac t e r i s t ics , na me ly those conne c ted wi th p l as t ic materi al s. Ther efore , t he

s i m p le d u m p i n g o f w as t es an d t h e i r co n seq u en t i a l b i o d eg ra d a t i o n i s n o l o n g e r co n v en i en t an d o t h e r

sys t ems are used , namely inc inera t ion .

I t i s e s t i m a t ed t h a t t h e p ro d u c t i o n o f d o m es t ic g a rb ag e am o u n t s t o 3 k g w eek -~ p e r so n -L , w h i ch

in a c it y of ha l f a mi l li on inhabi t an t s g ives som eth ing l i ke 1500 tons of garbag e pe r week . Wi th

an averag e spec i fi c g rav i ty o f 960 kg m - 3 (E n v i ro n m en t a l C o n t ro l an d P u b l i c H ea l t h C o u r se T eam ,

1974) for t he domest i c garbage , t he vo lume tha t i t occupies ranges 10 ,000 m 3 a v a l u e t h a t sh o w s

t h e i m p o r t an ce o f t h e p ro b l em t o b e d ea l t w it h , sp ec ia l ly w h en o n e a t t a ch es t o t h is v o l u m e p ro b l em

the e f fec ts on p ubl i c hea l th , w hich i s se r ious ly enda ngere d i f no ser ious s t eps a re t aken for t he

p ro p e r d i sp o sa l o f t h e w as t e s .

Al so ac cord in g to t he ab ov e re fe rence (1974) c i rca 20~o of t he to t a l weight o f t ow n ga rbages i s

co m p o se d o f v eg e t ab l e p ro d u c t s an d d eg rad ab l e m a t e ri a ls . T h ese , b e in g su b j ec t t o b ac t e r ia l

b i o d eg rad a t i o n g i ve ri se t o n o x i o u s g a se s an d u n p l ea san t sm ells , an d co n s t i t u t e fo o d fo r r a ts an d

i n sec ts , b e in g a co n s t an t h aza rd t o t h e p u b l i c h ea l th an d a n u i san ce t o t h e n e i g h b o u r co m m u n i t ie s .

In t h is scenar io , t he par t i cu l a r case of hosp i t a l s appears . Here , t oge ther wi th the dom est i c was t es ,

t here a re o ther w as t es wi th spec if i c charac t e r i s t i cs such as organ ic was t es , band ages , e t c. h igh ly

co n t am i n a t ed , t h a t r eq u i r e sp ec i a l m an i p u l a t i o n ca re s , n am e l y t h e n eed t o av o i d t r an sp o r t a t i o n

out s ide the hosp i t a l p remises , and the need to t rea t t hem wi th in s t r i c t san i t a ry condi t i ons . These

req u is i te s m ak e t h e u se o f in c i n e ra to r s l o ca t ed i n th e h o sp i t a l a r ea m a n d a t o ry .

T rad i t io n a l l y , n o h ea t r e co v e ry f ro m su ch i n c in e ra t io n p l an t s w as p e r fo rm ed . P re sen t ly , w i t h t h e

energy c r i s i s , t he t rend i s t o recover t he was t e gas hea t , namely to produce hot water .

In t he presen t tex t , an acco un t is g iven as t o t he deve lop me nt of t rad i t i ona l i nc inera t ion p l an t s

i n o rd e r t o r e co v e r w as t e g a s h eat , an d so m e ex am p l e s a r e sh o w n o f ap p l i c a ti o n s u n d e r w ay .

T R A D I T I O N A L I N C I N E R A T I O N P L A N T S I N

P O R T U G U E S E H O S P I T A L S

In Por tuga l , each hospi t a l has i t s own inc inera t ion p l an t , genera l ly wi th two inc inera tors . Up

to 1975 the p l an t s were des igned wi th the inc inera tors h aving ind iv idua l exh aus t sys t em s wi th gas

385


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386 J A BOAVIDA ROQUEe t a l

Jnclnero tor

2 WO sl l~ : j Of fenD er

- - i T C h , m n e y

Fig 1 No rm al inc inera t ion plant used in Portugu ese hospi ta ls unt i l 1975 S chem atic representauo n

w ash i n g , so t h a t t h e g a se s a t th e o u t l e t o f t h e s t a ck sh o u l d h av e t h e fo l lo w i n g m ax i m u m v a l u es :

S o l i d p a r t i c l e s - -1 5 0 n ag m -3 ; C a rb o n d i o x i d e (C O 2) --12 ~ /o ; C a rb o n m o n o x i d e (C O ) - -0 .5 ~ o .

F i g u re 1 is a s ch em a t i c r ep re sen t a t i o n o f a n o rm a l p l an t.

I N C I N E R A T I O N P L A N T S W I T H H E A T R E C O V E R Y

The pe t ro l e um cr i s i s i n 1973 , and spec i f i ca lly the seco nd 'sho ck ' i n 1978/79 (as a re su i t o f t he

I r a n / I r a q w a r ) w e r e v e ry i m p o r t a n t f o r P o r t u g a l , a s P o r t u g a l i m p o r t s f r o m t h is s o u rc e a b o u t 9 0 %

o f i ts p r i m a ry en e rg y , b e i n g t h e e f f ect o f t h e o il in c rea se s t h e re f ro m v e ry s ig n i fi c an t i n t h e C o u n t ry ' s

B a l an ce o f P ay m e n t s an d ex t e rn a l d e f ic i t.

T h e sav i n g o f en e rg y i n g en e ra l b ecam e t h e re fo re m an d a t o ry , b e i n g t he r eco v e ry o f t h e h ea t f ro m

w as t e g a se s o f i n c i n e ra t i o n p l an t s o f h o sp i t a l s o n e o f t h e p o ss i b l e w ay s o f s av i n g en e rg y .

A s a s i gn i fi c ant am o u n t o f en e rg y i s u sed i n h o sp i t a ls t o h ea t w a t e r , i t w as co n s i d e red i n t e r e st in g

t o s t u d y t h e e r ec t io n o f h ea t r e c o v e ry sy s t em s f ro m t h e co r r e sp o n d i n g i n c i n e ra ti o n p l an t s fo r t h a t

p u r p o s e

A P P R A I S A L O F T H E E C O N O M I C A L F E A S I B I L I T Y O F H E A T

R E C O V E R Y F R O M I N C I N E R A T I O N P L A N T S IN


B as i c d a t a

(1) t h e i n c i n e ra t i o n o f g a rb ag e i n h o sp i ta l s i s a m u s t , w h e t h e r h ea t i s r e co v e red o r n o t ;

(2 ) i t i s co n s i d e red p o ss i b l e t o r e co v e r 5 0 % o f t h e en e rg y p ro d u ced i n su ch i n c i n e ra t i o n , w i t h

ad eq u a t e h ea t ex ch an g e r s ;

(3) t he ho spi t a l co ns ide red has the s ize of a d i s t r i c t hosp i t a l , i .e . wi th an av erage o f 500 be ds ;

(4) t he hospi t a l garbage has the fo l lowing average charac te r i s t i cs : humidi ty- -70%; dens i ty- - - -0 .3 ;

i n c o m b u s t i b le s o l i d s - - 5 % ; h e a t c a p a c i t y - - 1 2 . 6 k J k g - 1:

(5 ) t h e h o s p it a l h a s a n a v e r a g e o f : n u m b e r o f b e d s - - 5 0 0 ; p r o d u c t i o n o f g a r b a g e - -

2 k g b e d . d a y - t ; n o r m a l w e e k l y w o r k i n g h o u r s - - - 4 0 h ; e f f ic ie n cy o f t h e w o r k o f lo a d o f t h e

i n c i n e ra t o r s - -8 0 % ; t im e o f b u rn i n g p e r l o ad 1 h ; n u m b er o f i n c i n e ra to r s in u se 2 ; s an i t a ry h o t

w a t e r c o n s u m p t i o n - - - 1 20 I t b e d . d a y - t; t e m p e r a t u r e o f c o l d w a t e r f r o m m a i n s - - 1 0 ° C ; t e m p e r a t u r e

o f h o t w a t e r t o u se - - -6 0 ° C .

B ased o n t h e ab o v e d a t a , t h e i n c in e ra t i o n p l an t sh o u l d h av e t h e fo l l o w i n g ch a rac te r is t ic s :

c a p a c i t y o f e a c h i n c i u e r a t o r - - 1 6 0 k g l o a d (h ); p o w e r o f th e b u r n e r s o f t h e i n c i n e r a to r - - 2 . 3 5 k W ;

t o ta l c o m b u s t io n p o w e r - - 9 2 8 k W .

A cco rd i n g t o (2 ) ab o v e , t h e am o u n t o f en e rg y r eco v e red i s e s t i m a t ed t o b e 7 .7 x lOS k W h .

O n t h e o t h e r h a n d t h e a v e r ag e a n n u a l c o n s u m p t i o n o f en e r g y f o r w a t e r h e a t i n g i s e s t im a t e d t o

be 12.7 x 105 kW h.

T h e re fo re , t h e h ea t r e co v e red a l lo w s fo r an eco n o m y o f 6 0% o f t h e co n v e n t i o n a l en e rg y u sed

fo r h ea t in g t h e w a t e r . F ro m t h e eco n o m i ca l p o i n t o f v i ew , th e co n d i t i o n t h a t m ak es t h e h ea t

r eco v e ry sy s tem fea s i b l e i s t h a t t h e co r r e sp o n d i n g i n v es t m en t ( a t M ay 1 98 2 v a l u e s, e s t im a t ed t o

b e 1 8 00 ,0 00 e s cu d o s ) sh o u l d h e sm a l l e r t h an t h e g en e ra li z ed co s t o f s av ed en e rg y , c a l cu la t ed b y

t h e f o r m u l a

C C E C E x C c x F


3/4

T h e i n c i n e r a ti o n o f h o s p i t a l w a s t e s 3 8 7

I I n c i n e r o t o r

H e Ot e x c h a n g e r

Washing chomber

4 Chimney

F i g . 2. I n c i n e r a t i o n p l a n t w i t h h e a t r e c o v e r y . S c h e m a t i c r e p r e s e n t a t i o n .

w h e r e CCE cost o f t h e co n se rv ed en e rg y ; C E - -a n n u a l v a l u e o f t h e co n se rv ed en e rg y ; C , , --u n i t

co s t o f en e rg y ; F - -u p d a t i n g f ac t o r o f co s t, g iv en b y t h e fo rm u l a .

( 1 + i ~ F 1 = ( 1 + i ~ N

F = V _ i L \- --~1

_

where : i - - -cap i t a l ra t e of in t e res t; j - - -c os t o f energy ra t e o f i ncrease ; N-- -de prec i a t ion per iod or

average l i fe .

C o n s i d e r i n g t h a t t h e co s t o f en e rg y in c rea ses 5 m o re t h an t h e av e rag e co s t o f liv in g an d t h a t

C e = 1 . 9 0 E s c / k W h ( M a y 1 98 2)

N =

10

one can ca l cu la t e t he genera l i zed cos t o f saved energy to be 11 ,700,000 escudo s , i. e. ab ou t s ix and

a ha l f t imes more than the foreseen inves tment . Being prac t i ca l ly a l l t he equipment i ns t a l l ed for

t h e h ea t r e co v e ry m ad e i n P o r t u g a l , an d co n s i d e r i n g t h a t t h e s av ed en e rg y r e su lt s f ro m i m p o r t ed

fue l , i t i s easy to conf i rm the economica l feas ib i l i t y of t he pro j ec t .

I N C I N E R T I O N P L A N T S W I T H H E A T R E C O V E R Y U S E D I N


T h e ad o p t ed p l an t s h av e i n t h e ex h au s t g a s c i r cu i t - -o b v i o u s l y b e fo re t h e w ash i n g ch am b er - - a

co u n t e r cu r r en t t u b u l a r h ea t ex ch an g e r , w i t h g a s t em p e ra t u re s o f 8 0 0 ° C o u t l e t (d e s ig n v a l u e s) .

T a b l e I

H o s p i t a l

J u l i a d e

A b r a n t e s B a r r e i ro V i la R e a l M a t o s

T y p e o f

h o s p i t a l D i s t r i c t D i s t r i c t D i s t r i c t P s y c h i a t r i c

N o . o f b e d s 3 5 0 5 0 0 5 0 0 1 5 0 0

D a i l y a v e r a g e 2 k g b e d - t 2 k g b e d - t 2 k g b e d - i 1 k g b e d - i

g a r b a g e

w e i g h t b e d - i

T o t a l w e i g h t o f 4 9 0 0 k g 7 0 0 0 k g 7 0 0 0 k g 1 0 ,5 0 0 k g

g a r b a g e w e e k

I n c i n e r a t o rs T w o i n c i n e r a t o rs T w o i n c i n e r a to r s T w o i n c i n e r a to r s T w o i n c i n e r a to r s

o f 1 2 0 k g l o a d - I o f 1 60 k g l o a d - t o f 1 60 k g l o a d - i o f 2 0 0 k g l o a d - i

B u r n e r o f g a s o i l B u r n e r o f g a s o i l B u r n e r o f B u r n e r o f

p r o p a n e g a s t h i c k - f u e l- o i l

H e a t T w o c o u n t e r c u r r e n t O n e c o u n t e r c u r r e n t O n e c o u n t e r c u r r e n t T w o c o u n t e r c u r r e n t

r e c o v e ry h e a t e x c h a n g e r h e a t e x c h a n g e r h e a t e x c h a n g e r h e a t e x c h a n g e r

r e c o v e r y u n i t s f o r r e c o v e r y u n i t f o r r e c o v e r y u n i t f o r r e c o v e r y u n i t f o r

h o t w a t e r p r o d u c t i o n h o t w a t e r p r o d u c t i o n h o t w a t e r p r o d u c t i o n l o w p r e s s u r e

1 0 - 6 0 ° C ) 1 0 - 7 0 ° C ) 1 0 -- 7 0° C ) h o t w a t e r p r o d u c t i o n

7 0 - 9 5 C )

A n n u a l p r e d i c t e d 5 . 4 x 1 0 k W h 7 . 7 x 1 05 k W h 7 . 7 × 1 05 k W h 1 .2 x 1 06 k W h

e c o n o m y


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388

J. A. BOAVIDA ROQUE e t a l

Table 2.

Temperature in Temperatur e at Temerature at

combustion inlet of outlet of

Day Readin g chamber exchanger exchanger

2 ~ 700 440 220

3 ~ 750 500 240

a 900 600 300

2 l 840 420 120

2 ~ 900 500 200

3~ 940 580 220

4~ 1000 640 260

3 1~ 840 420 180

2~ 800 500 300

3~ 900 600 260

4 800 560 220

4 I n 740 420 100

2~ 800 500 180

3~ 700 480 200

4 ~ 900 600 240

Figure 2 is a schematic representation of the designed installations. Such systems were installed

in Portugal in the District Hospitals of Abrantes, Barreiro, Santar~m and Vila Real, and also in

the Psychiatric Hospital Jfllio de Matos , in Lisbon in this case for production of low pressure hot

water) and have the design characteristics gwen in Table 1.

Of these installations only the one from the Hospital in Vita Real is working at full capacity,

the others being under commission.

OBSERVED RESULTS

As per above, only the Vila Real Hospital heat recovery plant is working. The fa~t that it is the

only one, together with the fact that it has been working for a short period, does not allow yet

for a global evaluation of the obtained savings. Nevertheless we can discuss some of the results

obtained, namely in what regards the temperatures of the combustion gases and the corrosion

problems that appeared.

As for gas temperatures the values of the measurements performed in four successive days are

presented in Table 2.

The temperatures registered deviate from the design values, and also the amount of garbage per

c pit was in some cases much less to the design values--these obtained from the foreign literature

available. There has also been found accelerated spot corrosion in the tube bundle.

FINAL CONSIDERATIONS

The heat recovered from exhaust gases of incinerators in Portuguese hospitals is likely to be used

in the production of sani tary hot water, with up to 60~o savings in the energy used to heat these

waters, with the corresponding investments having a payout time of 4-5 yr. Nevertheless, the first

industrial results obtained show that the design values were overestimated and that unpredicted

corrosion problems took place in the heat exchanger installed.

The plants repair is being prepared, as well as the studies that will allow us:

1) To find the causes of the corrosion phenomena in the tubes by metallurgical analysis of these

and by analysis of the gases.

2) To change the type of combustion, trying to perform the burning by pyrolysis, in order to

increase the combustion temperature and to reduce the corrosive agents over the tube bundle.

3) To increase the temperature of the gases at the entrance o f the heat exchanger- -by decreasing

largely the heat losses between the combustion zone and the heat exchanger.

The changes under study correspond to a further investment, which nevertheless is considered

advantageous, even though a higher pay-off time would be expected.

H E A T R E C O V E R Y I N T H E I N C I N E R A T I O N O F H O S P I T A L W A S T E S

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